Layers of dielectric film are used in several applications in sub-micron integrated circuits (ICs) fabrication. Four such applications are shallow trench isolation (STI), premetal dielectric (PMD), inter-metal dielectric (IMD) and interlayer dielectric (ILD). All four of these layers require silicon dioxide films that fill features of various sizes and have uniform film thicknesses across the wafer.
Chemical vapor deposition (CVD) has traditionally been the method of choice for depositing conformal silicon dioxide films. However, as design rules continue to shrink, the aspect ratios (depth to width) of features increase, and traditional CVD techniques can no longer provide adequately conformal films in these high aspect ratio features.
Two alternatives to CVD are atomic layer deposition (ALD) and rapid vapor deposition (RVD). ALD methods involve self-limiting adsorption of reactant gases and can provide thin, conformal dielectric films within high aspect ratio features. ALD methods have been developed for the deposition of silicon oxide film. RVD processing (also known as pulsed deposition layer (PDL) processing) is similar to ALD in that reactant gases are introduced alternately over the substrate surface. An ALD-based dielectric deposition technique typically involves adsorbing a metal containing precursor onto the substrate surface, then, in a second procedure, introducing a silicon oxide precursor gas. The silicon oxide precursor gas reacts with the adsorbed metal precursor to form a thin film of metal-doped silicon oxide. In RVD the silicon oxide film can grow more thickly. Thus, RVD methods allow for rapid film growth similar to using CVD methods but with the film conformality of ALD methods.
The cost of chemicals needed to deposit a given amount of oxide is inversely proportional to reactant conversion. Reactant conversion in a RVD reactor is typically significantly lower than one and is dependent on process conditions. Thus, in conventional RVD (and ALD) reactors, a significant amount of the silicon-containing precursor is not utilized. Because conformal deposition processes require reactants of high purity, recovering the silicon-containing precursor in a recycle stream is impractical. Unreacted precursor is lost. In addition, the amount of oxide deposited for a given dose of metal-containing precursor is limited, requiring more metal-containing precursor.
What is therefore needed are improved methods for forming conformal films that reduce the amount of metal-containing precursor and/or silicon-containing precursor required to deposit a given amount of film on a substrate.